The invention generally relates to computer systems and, more particularly, the invention relates to displaying television signals on computer display devices.
The National Television Standards Committee sets the standards for television signal transmission (the xe2x80x9cNTSC standardxe2x80x9d) in the United States. In particular, the NTSC standard requires that a television signal include sixty interlaced half-frames for each second of a motion picture displayed by a television. To that end, a television signal in the United States includes a sequential series of alternating xe2x80x9coddxe2x80x9d half-frames and xe2x80x9cevenxe2x80x9d half-frames that are to be displayed on respective odd and even lines of a television display. Upon receipt of a television signal in which the first half frame is odd, for example, a television draws the entire first odd half-frame, followed by the entire first even half-frame, followed by the entire second odd half-frame, etc . . .
As is known in the art, a television includes a phosphor element on a display face of a cathode ray tube, and an electron gun for energizing the phosphor as specified by a received television signal. The energy emitted by the energized phosphor element produces a visible display of the television signal. The total time that elapses between the time that the phosphor is first energized, and the time that the energy in the phosphor dissipates (known as xe2x80x9cphosphor persistencexe2x80x9d) is the entire time that a half-frame is viewable on a television display face. Typically, a half-frame is drawn while an immediately preceding half-frame is fading, but still visible. Together, the faded preceding half-frame and the half-frame being drawn produce a motion picture effect upon the display face of the cathode ray tube.
Unlike televisions, computer monitors draw entire frames instead of a series of half-frames. Specifically, a computer monitor is configured to consecutively draw each line on a monitor display face and thus, no lines on a computer monitor are skipped. Moreover, phosphor elements in a computer monitor typically have a much lower phosphor persistence than those in a television, thus enabling more frames to be displayed by a monitor each second. For example, many known types of computer monitors can draw sixty full frames each second while a television can only draw sixty half-frames each second. Accordingly, use of a television signal for display by a computer monitor typically does not produce the quality that a television signal produces on a television since half frames fade too rapidly on a computer monitor.
In accordance with one aspect of the invention, an apparatus and method for displaying a television signal on a computer monitor first receives a selected first field data block of the television signal for display by the monitor. The television signal preferably includes a stream of first field data blocks and second field data blocks that are intended for display by respective first and second sets of lines on the computer monitor. After receipt of the first field data block, an immediately preceding second field data block is faded to produce a faded second block. The faded second block then is displayed on the second set of lines of the monitor, and the first field data block is displayed on the first set of lines of the monitor.
In accordance with another aspect of the invention, the first field data block has an immediately following second field data block that is displayed on the second set of lines after the faded second block is displayed by such lines. The first field data block also may be faded to produce a faded first data block that is displayed on the first set of lines after the first field data block is displayed by such lines. The faded first data block preferably is displayed at the same time as the immediately following second field data block.
In preferred embodiments, the first field data blocks include even field line data and the second field blocks include odd field line data. The first set of lines thus are even lines and the second set of lines thus are odd lines. In other embodiments, the first field data blocks include odd field line data and the second field blocks include even field line data. The first set of lines thus are odd lines and the second set of lines thus are even lines.
In yet other embodiments of the invention, the television signal is in a NTSC (National Television Standards Committee) format or in a PAL (phase alternating line) format. In some embodiments, the immediately preceding data block is faded by first retrieving such data block from a front buffer in a double buffer frame buffer, and then applying alpha blending to such data block to produce the faded second block. Once produced, the faded block is copied into a back buffer of the frame buffer.
In accordance with another aspect of the invention, and apparatus and method of processing a television signal for simulating a television image on a computer monitor selectively fades data blocks. The television signal includes a stream of alternating first and second data blocks. More particularly, a first data block and second data block are received at an input. The first data block immediately precedes the second data block in the television signal. The first data block then is faded to produce a faded first data block. The faded first data block then is combined with the second data block to produce a frame. The frame then is forwarded to the computer monitor.
Alternative embodiments of the invention are implemented as a computer program product having a computer usable medium with computer readable program code thereon. The computer readable code may be read and utilized by the computer system in accordance with conventional processes.